1. Field of the Invention
This invention concerns lubricants and methods for their production. More particularly, lubricating oils having enhanced viscosity properties are made by combining certain dispersant viscosity index improver and detergent lubricant additives.
2. Description of Related Information
Lubricants play an essential role in many areas, particularly in the transportation industry. Large amounts of inexpensive lubricants are needed to keep transportation vehicles running smoothly. Mineral oils are relatively inexpensive and have been used effectively as lubricants. The use of mineral oils is, however, curtailed by the limited performance characteristics of mineral oils over the full range of temperature and conditions under which lubricants are used, such as for lubricating engines or other high speed, moving parts. Lubricants often need to have sufficient fluidity, which can be determined by measuring viscosity, over a wide temperature range. For example, engine crankcase lubricant needs to be sufficiently fluid at temperatures well below 0.degree. C. to enable engine start-up in cold weather. Conversely, such lubricant must also have enough viscosity at high temperatures during engine operation to avoid "thinning out", which would result in loss of engine lubrication.
Synthetic oils have been developed which can operate more effectively over a wider range of conditions than mineral oils alone. Various additives have also been developed which supplement and extend lubricating oil performance. Additives called viscosity index, or "VI", improvers or modifiers, are designed to improve the viscosity of lubricants, such as by increasing, or extending, the viscosity of the lubricant at higher temperatures. For example, U.S. Pat. No. 4,863,623 (Nalesnik) describes VI improvers which are polyolefins grafted with carboxylic groups derivatized with amino-aromatic polyamine. This VI improver also provides dispersancy and anti-oxidant properties.
These and other additives, like dispersants, detergents, anti-foamants, various inhibitors and more, are used to expand the utility of lubricants for differing applications. When used in combination, the additives and lubricants can interact in ways that change the properties and usefulness of the lubricant composition. For example, some dispersants and detergents have limited compatibility, such as disclosed in U.S. Pat. No. 4,502,971 (Robson) which describes mixtures of dispersants and magnesium detergents having increased viscosity which is reduced by prereacting dispersant with alkali metal salt. Similarly, U.S. Pat. No. 4,981,603 (Demange) describes a process for improving the compatibility of dispersants and magnesium detergents by premixing dispersant, detergent and solvent to eliminate haze and sediment.
Synthetic oils and additives, however, add significantly to the expense of lubricants. It would therefore be highly desirable if a lubricant can be made which maximizes the use of relatively inexpensive, mineral oils and minimizes the use of more expensive synthetic oils and additives, and which also gives more effective lubricant performance, such as better fluidity, over a wide range of temperatures and conditions.